F.4 數學題 ( 急! )

2008-08-24 5:53 am
計唔到 唔該幫我計一計 thz!!

1. find the values of k.

{ x^2 - 4y^2 + 20 = 0
{ x + 3y + k = 0

2. solve the following equations.

 3x - 開方2x+1 = 9 <-- (成個 2x+1 開方)

3. solve the following simultaneous equations using the algebraic method.

{ x^2 + y - x = 1
{ 2x + 3y = 1




answers :
1. k = +5 or -5
2. x = 4
3. ( -1/3 , 5/9 ) , ( 2 , -1 )

thank you !

回答 (1)

2008-08-24 9:26 am
✔ 最佳答案
2.
3x-√(2x 1)=9
3x-9=√(2x 1)
(3x-9)^2=(√(2x 1))^2
9x^2-54x 81=2x 1
9x^2-56x 80=0
X=4 or 2.2222.....

when x=2.222222...
LHS=3(2.22222)-√(2.2.222222) 1
=4.3333333

when x=4
LHS=3(4)-√(2.4)+1
   =9
so x=4

2008-08-24 01:31:58 補充:
when x=2.222222...
LHS=3(2.22222)-√(2.2.222222) 1
=4.3333333
=/=9(rejected)


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